PSK-31: Discovering digital mode on HF radio

Wikipedia defines PSK31 as: “Phase Shift Keying, 31 Baud”, a digital radio mode, used primarily in the amateur radio field to conduct real-time keyboard-to-keyboard informal text chat between amateur radio operators”.

This story begins on a warm and sunny early spring Sunday afternoon when I decided to explore PSK 31. I heard people telling stories about using PSK31 and thought to myself I would need a lot of extra-gear to be able to use PSK31, wouldn’t I? Turns out I don’t! I already bought a recent HF transceiver, one with all the I/O goodies needed to run PSK31. The Kenwood TS-590S has a USB port and you can do virtually anything thru this port, audio IN, audio OUT, radio control.

First things first. I watched some Youtube clips about this popular transmission mode.  K7AGE posted introduction clips on Youtube and that was enough to get me started. I download and installed the “Digipan” software K7AGE recommended, launched it, select my Audio I/O ports (Remember, everything can go thru the USB port on a Kenwood TS-590S), selected a popular PSK3 frequency (14.070 MHz) and voilà, instant results. There I was, reading dozens of simultaneous conversations, trying to learn the cryptic language used by PSK31 operators. One particular thing got my attention. Several operators mentioned they were using Ham Radio Deluxe’s Digimaster 780. I quickly download that “free” software, installed it and “Wow”, this is truly a complete software!

PSK 31 is used on specific frequencies on every amateur radio bands. On a given specific frequency, many stations around the world transmit tones on that same frequency. What helps PSK 31 determine a transmission from another is that on that same frequency, one stations might transmit a 300 MHz tone while another will transmit a 600 MHz tone. The tones are by themselves bit of data containing messages, or conversations. The PSK 31 software listens to all these tones simultaneously and differentiates the messages by isolating each tones into its own channel, therefor give the possibility of multiple and simultaneous transmissions on the same frequency. Get it? Well, now quite on the exact same frequency since the signals are separated by a tiny amount of bandwidth, the center of one signals might be at 14.0702 Mhz, the next one at 14.0705 Mhz and so on. You don’t have to move your VFO to listen to different frequencies since most HF transceivers will allow you to listen up to 5KHz of bandwidth from the carrier frequency, your audio card and your PSK31 software do all the work from there, most PSK31 transmission appears to be concentrated around 1000-1500 Hz anyway.

There I was, reading PSK31 chats for about an hour when I though to myself, I wonder how “transmitting” works exactly. I wasn’t terribly familiar with the software yet, but I decided to give it a try. I selected a frequency, not in the middle where all the action is, but on at the edge. 300 Hz will do just fine. I lowered my radio power output to only 5 watts, just in case someone was listening to this “newbie’s’ attempts to learn to operate PSK31.

No more than 2 seconds following the end of my first “CQ” transmission, a Netherlands stations replied back to my CQ… “What! Really?”… But I’m transmitting with only 5 watts of power on a terrible propagation day, could this be a fluke? Nope, the Netherlands station called me a second time. This is very interesting !

Then, I realized the potential of this transmission mode. It will go much farther with very little bandwidth and thus, help make tons of HF radio contacts around the world with very little equipment. The set-up was somewhat easy, the results were immediate.Anyone with a QRP (<5 watts) station and a small antenna could establish DX contacts with little efforts. I made some PSK31 contacts on frequency I did not suspect any PSK31 being present. Often signals are at or below the frequency’s noise level. I like this transmission mode and will bring more of my experiences to this blog.

Update – After using PSK for several months now, I can point out one thing which I truly dislike about digital modes; Macro-Keys. Most operators I made contacts with all use pre-programmed messages. This really kills the human approach to this digital sport. After seeing hundred of pre-programmed CQ calls and pre-cooked replies, it leads me to believe there is less to digital modes than I was led to believe. Since I can reach the outer most corners of the globe in telephony, I don’t see the point of pursuing this mode of transmission. I am, however, still very impressed by the digital mode’s ability to punch thru low propagation, frequency noise, band static and still deliver a message with very little antenna real-estate and/or transmission power. Many times, I would still receive messages when I couldn’t even distinguish the digital signals from the static white noise. It’s definitely an excellent QPR operation mode.

Some other reference work worth a look :


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